Multiplex communications – Wide area network – Packet switching
Patent
1986-12-05
1988-06-14
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 94, H04J 302, H04J 324
Patent
active
047517000
ABSTRACT:
A bus accessing method and apparatus for the practice thereof in a communication network is disclosed. The network comprises a transmit bus, a receive bus, a plurality of BIUs connected between the transmit and receive buses and a head-end for directing signals leaving the transmit bus onto the receive bus. Each information packet has two control bytes respectively following the start frame delimiter and preceding the end frame delimiter. Each BIU includes means for comparing the bits it receives with the bits as transmitted thereby, a bit mismatch indicating that a downstream BIU has been preempted. During packet transmission, upon detecting a bit mismatch, the transmitting BIU sets one or both control bytes to "1010" so that receiving BIUs in the network are apprised of the preemption. Subsequently, preempted BIUs transmit their packets in accordance with a predetermined protocol, each packet so transmitted having its control bytes set to "1010". In the case where there are no preempted BIUs, each BIU transmits a packet with the control bytes set to "0101", thereby apprising receiving BIUs that there are no preempted BIUs. Each free mode BIU with a packet to transmit commences transmission substantially immediately following the last transmitted packet if there are no preempted BIUs in the system and the buses are idle.
REFERENCES:
patent: 4516239 (1985-05-01), Maxemchuk
patent: 4517670 (1985-05-01), Ulug
patent: 4538261 (1985-08-01), Kume
patent: 4550401 (1985-10-01), Spears
patent: 4553235 (1985-11-01), Svensson
"A Fiber Optic Contention Bus with Bounded Delays", by M. E. Ulug, IEEE Journal on Selected Areas in Communications, vol. SAC-3, No. 6, Nov., 1985, pp. 908-915.
"Preemptive Contention Switch for Interconnecting LANs", by M. E. Ulug, Proceedings of IEEE MONTECH '86, Sep. 29-Oct. 1, 1986, pp. 26-29.
Burgujian Richard V.
Davis Jr. James C.
General Electric Company
Olms Douglas W.
Scutch III Frank M.
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